The variable infrared source near HH100

Photometric observations are presented which confirm the high variability, of up to 2.5 mag at K, of the IR source associated with the Herbig-Haro object HH100, and it is suggested that such a large variation must be a consequence of either (1) dramatic variations in the extinction of the source, due to the motions of a patchy circumstellar dust shell, or (2) fluctuations in the temperature of the underlying protostar. It is found that a two-component model of the source, comprising a hot star and an approximately 800 K dust shell, is required in order to account for the observations in terms of extinction changes alone. While distinguishing between the two interpretations is not possible on the basis of present data, the complications introduced by the extinction hypothesis point to intrinsic source variations.